This invention relates generally to gas turbine engine components, and more specifically to mounting of stators in turbine engines.
Gas turbine engines typically include a core engine having a compressor for compressing air entering the core engine, a combustor where fuel is mixed with the compressed air and then burned to create a high energy gas stream, and a first or high pressure turbine which extracts energy from the gas stream to drive the compressor. In aircraft turbofan engines, a second turbine or low pressure turbine located downstream from the core engine extracts more energy from the gas stream for driving a fan. The fan provides the main propulsive thrust generated by the engine.
An annular turbine nozzle is located between the combustor and high pressure turbine and between stages of the turbine. The turbine nozzle includes a pair of radially spaced inner and outer bands disposed concentrically about a longitudinal axis of the core engine and airfoils supported between the inner and outer annular bands. In the annular turbine nozzle assembly, the airfoils are arranged in circumferentially spaced relation from one another and extend in radial relation to the core engine axis. The annular turbine nozzle assembly is formed by a plurality of arcuate segments (alternatively referred to herein as “stator vane” or “stator vanes”) which fit end-to-end together to form the 360 degree circumferentially extending nozzle assembly. Each turbine nozzle segment includes arcuate segments of the inner and outer bands and one or more airfoils mounted between the inner and outer band segments.
The turbine nozzle provides the function of directing and/or re-directing hot gas flow from the combustor into a more efficient direction for impinging on and effecting rotation of the rotor stages of the turbine. The directing process performed by the nozzle also accelerates gas flow resulting in a static pressure reduction between inlet and outlet planes and creates high pressure loads and moments on the nozzle and its support system. Additionally, the turbine nozzle and its support systems also experience loads and moments due to the high thermal gradients from the hot combustion gases and the coolant air at the radial support surfaces.
In conventional nozzle support systems, the nozzle segments are attached by bolted joints or a combination of bolts and some form of clamping arrangement to an engine support structure. Such arrangements, however, create significant bending stresses in the nozzle and support due to mechanical loads and moments experienced by the nozzle airfoils and due to differential thermal expansion and contraction. Furthermore, holes required for receiving the bolts inherently create stress concentrations and may provide potential leakage paths. And, the nuts and bolts required for the assembly add undesirable weight to the engine and increase assembly and disassembly time.
In some designs of smaller turbine engines, turbine nozzles are supported only at their radially outer band in essentially a cantilever type arrangement since their radially inner band extends adjacent a rotating engine structure to which the turbine rotor stages are attached. In some stages, such as the first stage nozzle, the nozzle is attached to the engine stationary structure via a radially inner mount or flange structure coupled to the inner band. The radially outer band is not mechanically retained but is supported against axial forces by a circumferential engine flange. In other stages, such as stage 2 turbine of an engine, the turbine nozzle may be attached at its radially outer band but be free at its radially inner band. In either design, the use of bolts and clamps at circumferential locations about a turbine nozzle band act as a restriction to the band, which band is hotter than the structure to which it is attached, causing radial bowing of the outer band of the nozzle, causing out-of-roundness and stressing of the airfoils attached to the band. Such stressing of the airfoils may lead to formation of cracks in the airfoil.
A need exists for the development of alternative designs methods which will provide improvements in mounting and supporting stator components such as turbine nozzle segments to the engine support structure. Accordingly, it would be desirable to have a method and system for mounting static components in a turbine engine, such as a stator vane, to the engine support structure that react the loads and moments without using bolts and nuts. It is desirable to have a reaction mount system for a turbine stator component such that the stator can be easily replaced in an assembly.